Every 30 minutes all the blood in our bodies is filtered through two kidneys. But diabetes can cause these fist-size organs to fail, leading to a buildup of chemicals in the blood that would be fatal without dialysis or a kidney transplant.

At least 6,000 healthy people every year in the U.S. donate a kidney to someone they know, and about 100 more come forward to anonymously give the gift of glomeruli (the basic filtration units of the kidney). It’s true that you only need one kidney to live, but the operation required to remove its twin and the risk of disease developing in the remaining one later on make donation a serious decision.

Transplant surgeon Dorry Segev of the Johns Hopkins University School of Medicine studied mortality among 80,000 kidney donors during the past 15 years, comparing them with healthy people who have both kidneys. The study, published March 10 in the Journal of the American Medical Association—60 years after the first kidney transplant in the U.S.—found no increase in mortality among donors once they recover from the operation.

Although donors are carefully screened before the procedure, Segev emphasizes that there are risks: “It’s still a major operation. You’re still living with one kidney. People still need to think about it and be aware of the risks in taking on this heroic act.”